This is a proposal concerned with the problems of cardiac death and lethal arrhythmias. The major portion of the research continues the surveillance and follow-up of patients enrolled in registries accumulated under a contract "Sudden Cardiac Death and the Onset of Myocardial Infarction" (N 01 HL-12474) during 1971-1975, with surveillance and follow-up initially continued under a research grant "Sudden Death and the Onset of Myocardial Infarction" (HL-18805) during 1975-1978. From these registries large valuable data bases have been developed for the research projects. Various elements of the on-going aspects of the program have been called "Seattle Heart Watch", and this designation is used to describe certain activities in the proposal. The projects provide new information concerning the characteristics of heart disease and prognosis of survivors of sudden cardiac death, mechanisms and circumstances related to sudden cardiac death, development and evaluation of methods for providing earlier recognition of individuals at risk for having sudden death, cardiac pathology in sudden cardiac death, distribution of myocardial blood flow as assessed by radionuclide techniques, the possible role of platelet thrombi to arrhythmias and sudden death, detection and therapy of arrhythmias in sudden death survivors, long-term prognostic significance of clinical findings, coronary anatomy and ventricular performance in medically and surgically treated patients with coronary artery disease and the health status of survivors of sudden cardiac death. Studies of repetitive ventricular response to electrical and mechanical stimulation have been initiated to evaluate electrical instability in sudden death survivors.